In connection with modern aircraft, a gas turbine engine generally includes a compressor section to pressurize an airflow, a combustor section to burn a hydrocarbon fuel in the presence of the pressurized air, and a turbine section to extract energy from the resultant combustion gases.
Bearings and an associated bearing compartment may be used to support the engine. A static structure associated with the bearing compartment is typically aligned/centered relative to a case structure of the engine. Providing for such aligning/centering allows for optimal clearance between rotating blades and rub strips. This clearance ultimately translates into performance/efficiency of the engine.
Threaded rods (also referred to as “I-rods” in the art) are used to radially position the bearing compartment structure relative to the engine case structure. A first end of the rods are attached to the bearing compartment structure and a second end of the rods are attached to the engine case structure. By adjusting the rods the bearing compartment can be radially shifted. Adjustments are obtained by pre-loading the rods on the second end (e.g., the end of the rods attached to the engine case structure) with one or more threaded nuts.
Referring to FIG. 2, a flowchart of a method 200 used for aligning/centering the bearing compartment structure relative to the engine case structure is shown.
In block 206, the bearing compartment is mounted onto the engine case structure.
In block 212, the threaded rods are pre-loaded.
In block 218, a frame (e.g., a main turbine frame) is attached to a mounting plate and centered on a turntable or rotary measurement device.
In block 224, a plurality of dial indicators/gauges are wired to one or more data acquisition machines from the bearing compartment and the engine case. The dial indicators/gauges are used to understand/interpret the centers of the bearing compartment and the engine case.
In block 230, the data acquisition machine provides data/information regarding the results of the centering based on the dial indicators/gauges. The data/information frequently takes the form of a plot and indicates which rod(s) to adjust (e.g., which nuts to turn).
In block 236, a determination is made whether the bearing compartment structure is aligned/centered to the engine case structure within a threshold/tolerance. If so (e.g., the “yes” path is taken out of block 236), flow proceeds to block 242 and the method 200 ends. Otherwise (e.g., the “no” path is taken out of block 236), flow proceeds to block 248.
In block 248, a technician adjusts the bearing compartment using one or more tools (e.g., a wrench). The adjustment of block 248 is based on the output provided in block 230 (e.g., an identification of which rod(s) to adjust). From block 248, flow may proceed to block 230; in this respect, a loop may be established between blocks 230, 236, and 248 until the centering/alignment is within tolerance.
The method 200 takes considerable time (e.g., two to three hours) to perform, frequently requires more than one technician, and is difficult to set-up. The results of the method 200 are not necessarily repeatable and rely on the judgment and experience of the technician.